[forwardport] fix(ios): make sure we can build an iOS release (#598) (#599)

This diff forward ports f47b0c6c16e0cd417e3591358eb85b45962f307d to master.

Original commit message:

- - -

1. we now need to name the framework `.xcframework` otherwise
gomobile refuses to build a new framework for us ¯\_(ツ)_/¯

2. remove duplicate errno definition for iOS (iOS and darwin
are considered the same, therefore we don't need iOS defs)

Reference issue for this PR: https://github.com/ooni/probe/issues/1876

This diff WILL need to be forwardported to master.

.github/workflows/ios.yml

@@ -13,4 +13,4 @@ jobs:
         with:
           go-version: "1.17.3"
       - uses: actions/checkout@v2
-      - run: ./mk OONI_PSIPHON_TAGS="" XCODE_VERSION=12.4 ./MOBILE/ios/oonimkall.framework.zip
+      - run: ./mk OONI_PSIPHON_TAGS="" XCODE_VERSION=12.4 ./MOBILE/ios/oonimkall.xcframework.zip